intercalando átomos de sodio en los llamados materiales de van der Waals. El avance se podría aplicar en tecnologías de la información y sensores biológicos de alta sensibilidad. SINC 4/5/2020 10:47 CEST

2D van der Waals layered oxides such as MoO 3 , V 2 O 5 , and WO 3. Given their vdW nature and thus compatibility with 2D vdW semiconductors, these 2D vdW oxides bear potential as high-κ dielectric materials for a facile integration with 2D vdW semiconductors for future 2D electronics and optoelectronics. [17,18] Specifically, MoO 3 is an attractive material to study due to its multifunctionality for many different applications. MoO 3

Layered transition metal oxides remain a relatively unexplored front in the study of two-dimensional (2D) van der Waals materials, providing opportunities to further advance semiconductor physics and devices in a novel class of atomically thin crystals. It is usually uncommon to observe tunable electronic characteristics or achieve field effect control in these materials, given their wide band gaps and insulating nature. However, when these oxides are manipulated via doping or intercalation with new ion species, the band gap, carrier concentration, and field effect mobility can be affected, as well. Herein, we conduct a study to dope multilayer nanoflakes of α-MoO 3 with H + ion intercalation, which creates oxygen vacancies and facilitates n-type conduction. Devices are characterized with controllable electron densities in the range of 10 19 − 10 21 /cm 3 and field effect gating behavior with typical field effect mobilities of 0.1 cm 2 /Vs. Furthermore, both wet-etching and dry-etching techniques are conducted to dope the lattice with F ions. It is found that fluorine doping is an effective reversible method to produce devices with enhanced ON−OFF switching capability during electrical gating. These advancements in controlling the n-type conductivity of nanostructured α-MoO 3 may further enhance its potential in various applications such as sensing, catalysis, or as flexible electrodes in batteries.

Transition metal oxides often possess complex interactions between charge, spin, lattice, and orbital degrees of freedom, resulting in correlated electronic and magnetic phases. Li x CoO2, one of the most commonly used cathode choices in rechargeable batteries, is a prime example of this, evidencing numerous correlated effects evolving as a function of lithium content (x). Due to the strong electrostatic forces that govern the layered nature of this material, however, most investigations of these behaviors have been on bulk forms (>0.1 mm). In the two-dimensional (2D) limit, correlated effects are more easily tuned and studied; therefore, it is of fundamental importance to develop an experimental basis for investigation. Herein, a two-step process is utilized to chemically delithiate and exfoliate LiCoO2 single crystals and study nanoflakes 10–60 nm thick, with 0.37 < x < 0.8. An initial electrical characterization of this new form reflects bulk conduction properties, verifying the reliability of this new technique: temperature-dependent resistance measurements indicate an insulating 2D variable ranging hopping conduction for samples of x > 0.75, and metallic characteristics with a finite residual conductance for x < 0.75. However, these thin flakes also exhibit correlated characteristics less commonly observed and understood in Li x CoO2. An energy barrier upon contact formation is observed for all conditions, independent of lithium concentration and electrode work function, suggesting enhanced correlated effects due to reduced dimensionality. Additionally, charge-ordering phenomena in the temperature-dependent resistance occur under specific preparation conditions. These anomalies are markedly larger in magnitude than previous accounts in bulk systems and are also found in low lithium ranges of x < 0.5, matching theoretical predictions not commonly observed experimentally. This work utilizes a new approach to gain insight behind the complex transport phenomena inherent in Li x CoO2, providing a new opportunity to understand these correlated effects using a 2D, single-crystal form.

for electronic devices. Oxides constitute a broad family of materials with a wide range of potential applications, from catalysis to electronic, photonic, ferroelectric, magnetic and multiferroic functionalities. Understanding structure-property relations in free-standing, supported, and confined two-dimensional ceramics or "ceramic flatlands" has been identified as one of the challenges for future work in ceramics by a recent National Science Foundation workshop. [9] Nonetheless, over the last decade, there have been many reviews on 2D oxides either as the main focus or as a part of a more general nano-materials focused review papers or books. One of the earlier reviews of nanosheets of oxides and hydroxides focused on synthesis, properties -especially photon-induced behavior -and their assembly, was published in 2010 by Ma et al. [11], followed by a second review [12] as a part of a special issue on "2D Nanomaterials beyond Graphene" in 2015. Around the same time (2011) another review by Mas-Balleste et al.[13] also emphasized the importance and variety of 2D oxides. A more recent focused review on 2D oxides can be found in 2019 paper of Hinterding et al.